Process for the hydrolysis of cellulose acetate



Patented May 10, 1932 UNITED HARRY L 3 AY AND CYBILYJSTAUD, FA QHE ER,NE YQBK'AN EE B E s. WEBBER, or SPRINGFIELD,-EIJLASSACHUSETTS, ASSIGNQRSJD EAs'rMaN 3on4 QM NYY CHE ER, NEW YO econnonnrxon: os nnw yoga ra emesFOR rim eY-nnomsrs for YQELLULQ$E semen No'Drawing,

'This-invention relates to a process for the hydrolysis of: celluloseacetate and particularly to the hydrolysis of cellulose acetate-in thepresence of ethylene chloride, also k'nown as ethylene dichloride.

Cellulose triacetate as produced by the usual processes, of,--fo'rexample, treating cellulosic material in acetic anhydride and aceticacidsolution containing acatalyst, is obtained in the fibrous femurthere-is -p resent in'theacetylating bath a suflicient amount of anon-solvent of the cellulose triacetate, and in the absence of such anon-solvent a cellulose triacetate which is soluble in the solution isobtained. The soluble triacetate is generally hydrolyzed by simplydestroying the anhydride, which has not reacted with the cellulose, withwater and adding thereto a hydrolytic catalyst and holding the resultantsolution until an acetone soluble product is obtained. The hydrolysis ofthe fibrous cellulose acetate, however, as well as precipitatedcellulose triacetate, which, in.

none of them have proven commercially important. Owing to the limitedavailability of the acetic acid it is noweven more important thanformerly that a suitable method of hydrolysis be used that will decreasethe amount of acetic acid employed in the hydrolyzing bath.

An object of the present invention is to provide a process for thepreparation of acetone soluble cellulose acetate by the hydrolysis ofcellulose triacetate in the presence of ethylene chloride. A furtherobject of this invention is to conduct the deacetylation of thecellulose triacetate in a bath in which part of the acetic acid has beenreplaced by ethylene Application filed. December 14,1929. "SeriaYNo.414,208,

chloride. Other objects will hereinafter appear.

We have found :that a solution of ethylene chloride andacetieacid is agood solvent=for cellulosetriacetate. as well as the hydrolyzingcellulose acetatealthoughthe ethylene chloride alone is'not asolventperse-of either type of acetate. The ;use of this solvent mixture in ahydrolyzing 5 bath results in the production of a celluloseacetate ofexcellent quality in regard :to its viscosity, flexibility anddurability and it likewise, due-t0 its co st,}re-' duces -.consider ab1ythe expense of hydrolyzing eelluloseacetate. i v l v l/Ve have fou ndthat ethylene, chloride -ma y be present {a in as great" as percent "ofthe aceticacid present in the f hydrolyzi-ng 1 bath.While'ethyl'enechloride alone as statedfabove issncta solvent' forcellulose triacetate or *hydrolyzed celluloseacetate it becomes whenadmixed --with glacial acetic acid or other lower aliphatic organic acidsolvent-of all cellulose acetates down to the limit of'aeetonesolubility,;when there is as little as- '25- I hydrolyzing,- ingredientsacquired to carry outthis reaction suchas-wateroralcoholand tl1e=11sua1miner-al acid'or other type ofcatalystl i The hydrolysis; is preferablyconducted ,at a'temperature- 0f-approXimately 50 '6. and after a periodof-from- -18 to-Q l' hours the cellulose triacetate will be jfound to.have been hydrolyzedto a*solubility-3in-;acetone.v The whole solntion{may be either immersed or preferablyextruded into hot water which iskept at a temperature --we1labove-theiboiling pointof the ethylenechloride, (The ethylene chloride flashes innnediatelyfrom, the solutionand mayby suitable collecting and jcon-; densing means he recovered forfurther use while-thecellulose acetatewill 1 be found to have preeipitatedin a light flirfi'yform ,which can be i -'IE1dlly and 11efli'ciently washed and driedAJ 4 1 Vie shall now give anexample forcarrying outi ou'r- I invention but it; :will be distinctly understoo dthat we shall :not be limited g by the pr'oportion-s 01" details thereingiven except as they are indicated in the appended 7 claims.

i phoric acid (95%).

88 parts of cellulose triacetate, either the precipitated celluloseacetate which has been formed in a solvent .Iacetylating bath or thecellulose triacetate produced in fibrous form, is dissolved in a bathcontaining:

234 parts of glacial acetic acid, 312 parts of ethylene chloride, 26parts of water, 23 parts of sodium acidsulfate'monohydrate, .9 parts ofsulfuric acid, and 2.7 parts of phos- The cellulose"triacetate'willrapidly dissolve and after being placed in a suitable in acetone.

covered container at a temperature of approximately 50 C. and held for aperiod of 18 to22 hours under these conditions will produce, afterprecipitation in hot water and thorough washing and drying, a celluloseacetate of excellent quality which is soluble The ethylene chloridewill, of course, be flashed or vaporized when the hydrolizing bathcontaining it is introduced into the hot water precipitant and thevapors so produced may be recovered by collecting.

. and condensing them and by separation, all t in known manner.

While the hydrolysis may be'carried' out as described in the aboveexample, it is not, essential that the cellulose triacetate be in afibrous or precipitated form prior to this treatment, in as much as thehydrolysis may be conducted directly in an acetylation bath, in whichthecellulose acetate is invsolution, subsequent to the esterificationWithoutthe lose acetate in the presence of ethylene chloride and amineral acid catalyst.

3. In the process for the manufacture of cellulose acetate the stepwhich comprises hydrolyzing an acetic acid solution of celluloseacetatein the presence of ethylene chlo- When an acetone solubleproducthas been ob tained precipitating the hydrolyzed product inhot'water. p W

41 In the process for the manufacture of cellulose acetate the stepwhich comprises ride, a mineral acid catalyst and water andnecessity ofprecipitation and redissolving of I the precipitate prior to thehydrolysis. Our

treatment in this manner is particularly advantageous When used inconjunction with th'ejesterifying process described in the copendingapplications of H. Le B. Gray, Serial No.y24:0,94e3 and H. Le 13.. GrayandC. J. Staud, Serial 'No. 328,054. g

Various changes may be made in the proportions of ethylene chloride andglacial acetic acid employed providing the ratio of ethylene chloride toglacial acetic acid does not go above 4 to 1 as well as in theproportion or types of hydrolysts or catalysts used in thehydrolyzingbath or, for that matter, in

the degree of de-esterification of cellulose acetate obtained by thehydrolysis without departing fromthis invention or sacrificing any ofits advantages. 1

What we claim as new and desire to be secured by Letters Patent ofthe'United States 1. In the process for the manufacture of celluloseacetatethe step which comprises hydrolyzing an organic acid solution ofcellulose acetate in the presence of ethylene chloride. 2. In theprocess for the manufacture of cellulose acetate the step whichcomprises hydrolyzing an acetic acid solution of cellu-.

